Exemplary embodiments pertain to the art of electric machines and, more particularly, to a method of winding a stator core with a continuous conductor having a rectangular cross-section.
At present, many electric machines include stator cores that are wound with wire having a circular cross-section. The stator core is held stationary and the wire is fed through a winding needle that is rotated about a stator tooth. Once the stator tooth is wound, the wire is advanced to a subsequent stator tooth. At each tooth, the winding needle not only travels along a circular path but also moves in and out to layer the wire. Upon exiting the winding needle, the wire twists as a result of rotational forces developed while traveling along the circular path.
In other cases, the stator core is wound with wire having a rectangular cross-section. A continuous wire is laid into slot segments formed in the stator core. In this manner, the wire is not subjected to twisting. The use of rectangular wire increases a fill volume of the slot segments which, in turn, enhances electrical properties of the stator. Electrical properties of the stator are further enhanced by adding tooth elements to the slot segments. The tooth elements reduce torque ripples during start up of the electric machine. However, the tooth elements also create a localized narrowing of the slot segments. The localized narrowing precludes the use of a continuous wire having a rectangular cross-section. In such cases, the wire is formed into discrete sections or hairpins that are axially inserted into the slot segments. Once all sections are inserted, select ones of the sections are joined to form one or more phase windings for the stator.